The ability to properly chew and grind food is essential for nutrient digestion and absorption. Dysmastication is a condition involving impaired chewing- also known as mastication. [1]

Horses that are unable to chew properly may experience a cascade of problems affecting their nutritional intake, digestive system, and overall well-being. Horses with abnormal tooth wear or damaged or diseased teeth can also experience pain and discomfort. [2]

Diagnosing dysmastication involves observing the horse’s eating habits and conducting a physical examination. Additional diagnostic tools such as oral endoscopy, X-rays, and CT scans can provide further insights into a horse’s dental health.

Treatments for chewing disorders in horses may include:[5][2]

  • Dental floating
  • Tooth removal
  • Widening of tooth gaps
  • Surgical intervention
  • Pain management through medication

Dysmastication in Horses

Dysmastication in horses refers to any impairment or dysfunction in the chewing process. Horses with dysmastication may have difficulty chewing, or abnormalities in the way that they chew.

A horse’s teeth are essential for adequately grinding feed into smaller particles, a key step for efficient digestion. Any disruptions in a horse’s dentition can significantly impact their ability to eat and digest food properly.

Equine Teeth

Equine teeth are naturally adapted to their continuous grazing habits; growing continuously throughout their lives. Constant growth compensates for the wear and tear caused by chewing tough, fibrous plant materials, ensuring their teeth remain functional and effective for grinding feed.

However, this continuous growth can lead to imbalances if the teeth don’t wear down evenly. The diet and eating patterns of domestic horses might not provide the natural wear necessary, leading to uneven tooth wear.

Unfortunately, dental care for horses is often overlooked. Postmortem studies have frequently revealed undiagnosed dental issues in horses, highlighting a significant gap in equine healthcare. [15]

Signs and Symptoms

Signs of dysmastication or dental issues in horses can present in various ways including: [2]

  • Quidding: Dropping food from the mouth while chewing, often forming ‘balled up’ or ‘cigar-shaped’ masses.
  • Halitosis: Unpleasant breath odor.
  • Unusual facial expressions: Changes in facial expression may occur during chewing, potentially indicating pain or discomfort.
  • Weight loss: Loss of body condition ranging from mild to severe. Inadequate mastication can lead to reduced food intake and subsequent weight loss.
  • Changes in manure: Presence of long fibers in the feces, indicating inadequate digestion.
  • Behavioral changes: Irritability, reluctance to eat, or avoidance of specific types of feed. Affected horses may be resistant to having the bit placed in their mouth or respond to the bit negatively when ridden. Horses with dysmastication may also dip their hay in their water trough before eating it.
  • Excessive Salivation: Drooling or excessive production of saliva, potentially indicating oral discomfort.

Causes of Dysmastication in Horses

Dysmastication in horses can result from a range of factors, including poor tooth balance, dental disease, improper dental care, and systemic health problems.

Dental Issues

Dentition refers to the development, arrangement, and condition of teeth in a horse. It encompasses aspects such as the number, types, and structure of teeth, as well as their overall health and alignment within the mouth.

Horses are susceptible to a variety of dentition problems that can lead to difficulties in chewing. The risk of developing dental issues in horses tends to escalate with age.

Malocclusion

Dental occlusion refers to the way the teeth in the upper (maxilla) and lower (mandible) jaws contact one another. [1] In horses, the standard occlusion (orthooclusion) is described as a level incisor bite. [6]

A malocclusion refers to any deviation from a typical occlusion pattern. Malocclusions in horses are categorized into classes from 0 to 4, with Class 0 indicating normal occlusion​. [7]

Malocclusion can result from uneven wear, congenital defects, or improper dental care. Additionally, the formation of dental abnormalities such as hooks, ramps, enamel points, and wave complexes can contribute to malocclusion.​ [9][5]

Horses grind their feed in a lateral and rostral (back to front) motion. This can result in uneven wear on their teeth and the formation of malocclusions. [8]

These malocclusions can disrupt normal tooth movement and impair chewing efficiency. They commonly result in elongated cheek and incisor teeth due to abnormal wear patterns. This can also increase the risk of periodontal disease.​[6][9]

Misaligned Teeth

Misaligned teeth are a common cause of malocclusion, manifesting as: [9][5]

  • Overbites
  • Underbites
  • Rotations
  • Crowding
  • Displacements
  • Tilting in both the incisors and cheek teeth

Parrot Mouth

Parrot mouth is a type of malocclusion that can result in dysmastication. It occurs when the lower jaw (mandible) is shorter than the upper jaw (maxilla). [3][4]

Cheek Teeth Diastemata

Spaces between teeth should naturally be tightly pressed together. When the spaces between teeth are wider than normal, they can trap food and promote gum inflammation.

Diastemata are a primary cause of dysmastication in horses. [3] They can form due to developmental factors (such as misalignment or overcrowding) or acquired reasons (such as age-related reduction in tooth diameter). [3][13]

Sharp Dental Overgrowths

In domesticated horses, uneven tooth wear can lead to the development of points and pits on the molars. These dental irregularities can disrupt the natural chewing process, causing the horse to chew in a way that exacerbates the problem.

Prolonged tooth imbalances in horses can sharpen their molars into razor-like edges, potentially cutting into their cheeks and causing painful ulcers.

Wild horses typically experience fewer dental issues than their domesticated counterparts. This difference is largely attributed to their diet and grazing patterns.

In the wild, horses graze for many hours each day on rough forage and abrasive vegetation, which helps them naturally wear down their teeth more evenly.

Regular dental exams and tooth floating can help to maintain proper dentition and avoid sharp overgrowths.

Displaced Teeth

Overcrowding of teeth or irregularities in tooth alignment leads to overgrowths that can force teeth out of their natural position. [3]

Displaced teeth can cause soft tissue injuries in the mouth and contribute to the formation of gaps between teeth (diastemata). [10] The condition can also trigger periodontal disease and excessive growth of opposing teeth.

Tooth Fractures

Tooth fractures in horses are relatively rare, but when they do occur, they most commonly affect the incisors. These injuries are often due to falls, kicks, or oral play behaviours. [4] In many cases, fractured teeth are only identified after a small fragment of the tooth has been lost. [11]

Cheek teeth fractures are more commonly discovered without an apparent history of trauma. [11] Sometimes, fractures in cheek teeth can result from biting down on small stones in feed.

Fractures can also result from diseases affecting the dental pulp– the soft tissue containing blood vessels located in the center of the tooth. [1][3]

Loose fragments or sharp edges from fractures can cause discomfort during eating. In certain cases, the fracture exposes the tooth pulp, which can lead to infection. [3]

Infundibular Caries

Infundibular caries are decayed portions of the tooth caused by impacted feed. The acidic bacterial by-products from decaying feed can demineralize the hard dental tissue over time, making it more prone to fracture. [3]

Tooth Loss

Missing or damaged teeth can impair the grinding action required for proper mastication. In horses, tooth loss can occur due to:

  • Periodontal disease
  • Tooth decay with advancing age
  • Severe dental caries (cavities)
  • Trauma or injury to the mouth
  • Extraction by a veterinary dentist
  • Developmental or congenital abnormalities

Loose Teeth

Loosening of teeth due to aging, dental wear, or severe gum disease causes tooth movement during chewing, and stretching of the periodontal ligaments. [5] Loose teeth can result in pain and difficulty chewing.

Some loose teeth are not easily detected and may require dental forceps for identification. A painful response during routine floating procedures may indicate a loose tooth, necessitating further investigation.

Shedding of baby (deciduous) teeth begins around 2 1/2 years of age, and is typically completed by around 5 years of age. [3][16] Horses experiencing dysmastication around these times should be examined for loose deciduous teeth.

Wolf Teeth

Wolf teeth in horses refer to small, peg-like teeth that typically appear in front of the first premolar teeth in the upper jaw. [9] These teeth are vestigial, meaning they serve no practical function in a horse’s dental system.

Wolf teeth can cause pain and discomfort for horses when they come in contact with a bit. [9][5] This can lead to fractures or loosening of wolf teeth, causing further discomfort. [9]

Temporomandibular Joint (TMJ) Pain

The temporomandibular joint, commonly known as the “TMJ”, is the joint connecting the lower jaw (mandible) to the upper jaw (maxilla) via the temporal bone in the skull. The TMJ is comprised of interconnected tissues including:

  • Bone
  • Cartilage
  • Tendons
  • Ligaments
  • Muscles
  • Nerves
  • Blood vessels
  • Salivary glands

The TMJ is essential for chewing and communication between the horse and rider through the bit. TMJ issues in horses can lead to dysmastication due to pain or mechanical limitations. [2]

Causes of TMJ discomfort in horses include trauma resulting in partial dislocation, fractures, injury, arthritis due to long-term wear and tear, inflammation, infections, and muscle issues.

Dental Diseases

Dental disease in horses is addressed best if it is identified early and managed properly. Supportive care and regular veterinary or dentist evaluation can help to keep dental diseases in check.

Periodontal Disease

Periodontal Disease in horses is a condition that affects the supporting structures around their teeth. [1] Approximately 49% of horses are affected by periodontal disease. [1]

This disease involves inflammation or infection of:[12]

  • The gums (gingiva)
  • The periodontal ligament that attaches teeth to the jaw bone
  • Cementum (a calcified substance covering the roots of teeth)
  • The alveolar bone that holds the teeth in place

This disease is caused by bacteria accumulating at and below the gum line, leading to inflammation of the gums (gingivitis). Risk factors for periodontal disease include irregular dental wear, dental abnormalities, or traumatic injuries. [12][5]

If not addressed, periodontal disease can progress to periodontitis. In these cases the inflammation extends deeper, affecting the ligaments and bone supporting the teeth. [3]

Equine Odontoclastic Tooth Resorption and Hypercementosis

Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) is a dental condition that primarily involves the incisors and, occasionally, the nearby canine teeth. [3]

EOTRH is characterized by progressive dental resorption (dissolving or breaking down of tooth structure) and the abnormal deposition of cementum. [3] The condition is typically seen in horses 15 years and older.

Signs of EOTRH may include:

  • Swelling
  • Loss of tooth structure
  • Loosening of teeth
  • Gum inflammation or infection
  • Discomfort while eating or when pressure is applied to the affected teeth

In some cases, affected teeth might appear elongated, discolored, or have visible defects. [3]

Diagnosing EOTRH typically involves a dental examination by a veterinarian, which may include x-rays to assess the extent of the tooth resorption and changes in the affected teeth.

Oral Trauma

Mouth, tongue, or jaw injuries can lead to pain and discomfort while eating, resulting in dysmastication. [1] Excessive pressure from a bridle on the bars of the mouth or lips can also cause oral trauma that leads to dysmastication.

Although uncommon, horses can ingest foreign objects that get lodged in the mouth’s soft tissues and cause damage. [1] This can result in pain and chewing difficulties.

Complications Following Dental Treatment

Dental procedures can result in iatrogenic dysmastication, which is a form of chewing dysfunction directly caused by medical treatment.

Pain and difficulty in chewing can arise due to over-filing teeth, exposing sensitive structures, or applying excessive pressure during treatment. [2]

Widening of spaces between teeth during treatment can produce gaps between teeth and initially worsen dysmastication, leading to trauma of gums and periodontal tissues. [2]

The prolonged use of a full-mouth speculum is sometimes believed by horse owners to cause oral or temporo-mandibular joint (TMJ) pain. However, there is a lack of substantial evidence to support this claim, and TMJ issues are actually quite rare in horses. [2]

The use of orthodontic devices or wires for treatment of developmental conditions may cause oral trauma, but might not directly lead to dysmastication. Post-treatment dysmastication could stem from implant failure or fracture instability. [2]

Tumors or Oral Masses

Growth of tumors or masses (neoplasms) within the oral cavity can physically impede proper chewing and result in dysmastication. [3] Calcified tumours from dental tissues can also result in dysmastication. [4]

Unfortunately, oral tumors in horses often reach an advanced stage before horses show any noticeable clinical symptoms. [3] This often results in delayed diagnosis, underscoring the importance of regular dental check-ups for early detection.

To diagnose oral tumors, a comprehensive clinical examination is necessary, along with a dental exam. When possible, biopsies of suspected lesions should be performed. Computed tomography (CT) scans and other imaging techniques are extremely useful in identifying tumors that affect bones and teeth. [2]

Diagnosis of Dysmastication

Your veterinarian will diagnose dysmastication and identify its underlying causes through a physical examination and laboratory testing.

General Examination

They will request a detailed medical history of your horse, including any recent changes in body weight or behavior.

A complete physical examination of the head, neck, and gastrointestinal tract can be performed to rule out other potential issues and evaluate the horse’s overall health.

They may also want to observe your horse while eating to look for signs of pain, difficulty chewing, dropping food, or excessive salivation.

Dental Examination

A thorough oral examination is conducted, often under sedation, to assess the teeth, gums, and the oral cavity. High-resolution oral endoscopy may be used for a more detailed assessment. [1]

X-rays of the head are commonly used to evaluate tooth roots, jaw structures, and paranasal sinuses for abnormalities like infections or fractures. In complex cases, CT scans might provide more detailed images. [2]

Blood tests or oral swabs may be used to identify infections or systemic health issues contributing to dysmastication.

Treatment of Dysmastication

The treatment approach for dysmastication depends on the underlying cause of the chewing disorder.

Overarching treatment aims include:

  • Pain management
  • Correcting dental abnormalities
  • Restoring normal chewing function
  • Ensuring the horse receives adequate nutrition

Malocclusion

The treatment approach for malocclusion is depends on the severity of the issue. Treatments may involve extracting teeth and performing odontoplasty (floating or filing of the teeth). [3][4]

Diastemata

The primary goal of treating diastemata (gaps between teeth) in horses is to alleviate the associated pain from gum disease​​​​. [3][4] There are several methods for this, including the removal of trapped food using lavage and diastema forceps, followed by packing the gap with inert materials.

Another technique involves widening the spaces between teeth using a motorized burr. This method must be performed with care to prevent damage to the sensitive areas of the adjacent teeth. [13]

Overgrown Teeth

Sharp dental overgrowths can be reduced using odontoplasty. [2] Reductions must be done carefully to avoid damaging teeth by exposing or causing thermal injury to the neurovascular bundle (pulp horns).

Displaced Teeth

In cases where teeth are significantly displaced, tooth extraction may be the most suitable option. Additionally, managing any overgrowths on opposing teeth and addressing associated gaps in teeth is essential.

Fractured Teeth

Approaches to managing fractured teeth vary based on the type of fracture encountered. Loose dental fragments may require extraction. [14]

Loose Teeth

Treatment for loose teeth depends on how loose they are, tooth condition and any concurrent issues. Extraction is necessary for teeth with deep gum infections or loose deciduous and adult (senile) teeth. [2]

Sometimes reducing the height of the loose tooth and its counterpart can stabilize the attachments. [2] Managing gum disease by addressing diastemata, can also aid in firming up the attachments. [2]

Wolf Teeth

Removal of wolf teeth before a horse begins being bitted can prevent discomfort. [9]

Temporomandibular Joint (TMJ) Pain

Treatment options may include intra-articular medication, typically corticosteroids, or in severe cases, surgical procedures such as mandibular condylectomy. [2]

Periodontal Disease

Prompt treatment of dental diseases, caries, or gingivitis is crucial to alleviate pain, prevent periodontitis and restore normal chewing function. [12]

Treatment may include:

  • Comprehensive evaluation and cleaning of the tooth and surrounding tissues
  • Measuring the depth of periodontal pockets
  • Widening gaps between teeth to minimize food trapping

In advanced cases, tooth extraction may be necessary.

Equine Odontoclastic Tooth Resorption

EOTRH treatment may require extraction of severely affected teeth to alleviate pain and discomfort. Management of the condition necessitates regular dental care and monitoring to address emerging issues as the condition progresses.

Injuries

The treatment of traumatic oral injuries depends on the nature of the injury and extent of damage.

If a foreign object is lodged in a horse’s mouth, its removal by a veterinarian may be necessary to aid in recovery. Some objects may pass naturally. [2]

Iatrogenic Causes

Chewing dysfunction that occurs after dental treatment in horses may resolve spontaneously without additional intervention.

To minimize post-treatment dysmastication following procedures like widening spaces between teeth, your vet may use packing materials in the treated areas and provide pain relief. [2]

Tumors and Oral Masses

Management strategies for oral tumors and masses include surgical removal, topical chemotherapy, and radiotherapy, depending on the tumor’s type, size, and location within the mouth. [2]

Management of Chewing Disorders

Some horses affected by dysmastication improve with treatment, while others require long-term management of the condition to support their gut health and meet nutritional requirements.

Key aspects of management for horses with chewing difficulties include regular dental check-ups, dietary adjustments, and pain management.

Regular Dental Examinations

Scheduling regular dental check-ups with a qualified equine dentist or veterinarian is essential for the early detection and management of dental issues in horses.

It’s recommended that these examinations be conducted at least once or twice annually. Older horses and those with a history of dental issues may require more frequent care.

Routine procedures like filing or floating of teeth are crucial to prevent overgrowths, sharp edges, or malocclusions. These practices help maintain a proper grinding surface on the teeth, which is necessary for efficient chewing.

Feeding Management

Horses with dental issues may struggle to obtain the necessary nutrients from their regular diet due to problems with chewing and thus nutrient absorption. This can lead to deficiencies and weight loss.

An equine nutritionist can help you modify your horse’s diet to accommodate their dental issues while ensuring they receive balanced nutrition.

  • Feed Selection: Providing readily digestible feeds, such as chopped hay or extruded pellets, can ease the chewing process for horses with dental issues.
  • Grinding or Chopping Feed: Processing feeds into smaller, more manageable pieces can assist horses with chewing difficulties.
  • Soaking Feed: Softening feed by soaking it in water can make it easier for horses with dental problems to consume.
  • Fat Supplements: Underweight horses or hard keepers with dental issues benefit from oils and fat-based feeds to provide an energy-dense source of digestible calories.
  • Dietary Supplements: Incorporating supplements like vitamins and minerals can aid in maintaining overall oral health and compensate for any nutritional deficiencies.

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Pain Management

Pain management for dysmastication in horses is a crucial aspect of treatment, as dental issues often cause significant discomfort or pain.

Oral discomfort can worsen dysmastication complications like reduced appetite, decreased feed intake, and ineffective chewing.

  • Medication: Veterinary-prescribed pain relief medications may be necessary to alleviate discomfort associated with dental issues. Non-steroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone or flunixin meglumine are commonly used.
  • Behavioral Modifications: Providing a calm and stress-free environment during feeding times can encourage eating and reduce anxiety associated with dysmastication. Horses should be fed on their own to reduce competition for food.
  • Surgical Intervention: In severe cases if dental issues cannot be resolved through conventional methods, surgical procedures may be considered. Extraction of severely damaged teeth or removal of oral tumors might be necessary to alleviate ongoing dental pain.

Summary

  • Dysmastication or chewing disorders in horses can arise from various causes, significantly impacting their health and nutritional status.
  • Regular dental check-ups, ideally performed at least once or twice a year, are vital for early detection and treatment of potential dental problems that could lead to dysmastication.
  • Effective management of dysmastication requires collaboration between horse owners and veterinarians. Consult with your veterinarian to accurately diagnose and address the root causes of the condition.
  • Treatment of dysmastication may include pain management and dental procedures such as floating, tooth extraction, or correction of malocclusions.
  • Dietary modifications may be important to ensure they receive a balanced nutrition program. Work with an equine nutritionist to formulate an appropriate diet for your horse.

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References

  1. 7_Dental-Exam_TANNER.pdf. Accessed: Nov. 20, 2023.
  2. R. Reardon, Managing dysmastication in horses: an update. In Practice. 2018.
  3. H. Tremaine and M. Casey, A modern approach to equine dentistry 2. Identifying lesions. In Practice. 2012.
  4. D. O. Klugh, A Review of Equine Periodontal Disease.
  5. Dental Disorders of Horses – Horse Owners. Merck Veterinary Manual. Accessed: Nov. 18, 2023.
  6. How to Recognize and Clinically Manage Class 1 Malocclusions in the Horse. Accessed: Nov. 18, 2023. AAEP.
  7. Equine malocclusions: Are you overfiling?. DVM 360. Accessed: Nov. 28, 2023.
  8. B. A. Rucker, Equine cheek teeth angle of occlusion: how to calculate and clinical use for incisor shortening. Equine Veterinary Education. 2004.
  9. Common-Equine-Dental-Malocclusions.pdf. Accessed: Nov. 18, 2023.
  10. N. M. Collins and P. M. Dixon, Diagnosis and Management of Equine Diastemata. Clinical Techniques in Equine Practice. 2005.
  11. Equine-Dental-Disease.pdf. Accessed: Nov. 18, 2023.
  12. D. O. Klugh, Equine Periodontal Disease. Clinical Techniques in Equine Practice. 2005.
  13. B. A. R. DVM. Treatment of Equine Diastemata.
  14. P. M. Dixon, R. Kennedy, and R. J. M. Reardon, Equine ‘Idiopathic’ and Infundibular Caries-Related Cheek Teeth Fractures: A Long-Term Study of 486 Fractured Teeth in 300 Horses. Frontiers in Veterinary Science. 2021.
  15. P. M. Dixon, R. Kennedy, and R. J. M. Reardon, Prevalence and analysis of equine periodontal disease, diastemata and peripheral caries in a first-opinion horse population in the UK. Vet J. 2019.
  16. AAEP. The Importance of Maintaining the Health of Your Horse’s Mouth. American Association of Equine Practitioners. Accessed Dec 12, 2023.